With the advent of high speed xerographic copy reproduction machines wherein copies can be produced at a rate in excess of three thousand copies per hour, the need for a document handler to feed documents to the copy platen of the machine in a rapid, dependable matter was recognized to enable full utilization of the reproduction machines potential copy output. A number of document handlers are currently available to fill that need. These document handlers must operate flawlessly to virtually eliminate the risk of damaging the originals and generate minimum machine shutdowns due to uncorrectable misfeeds or document multifeeds. It is in the initial separation of the individual documents from the document stack where the greatest number of problems occur.
Since the documents must be handled gently but positively to assure separation without damage through a number of cycles, a number of separators have been suggested such as friction rolls or belts used for fairly positive document feeding in conjunction with a retard belt, pad, or roll to prevent multifeeds. Vacuum separators such as sniffer tubes, rocker type vacuum rolls, or vacuum feed belts have also been utilized.
While the friction roll-retard systems are very positive, the action of the retard member, if it acts upon the printed face can cause smearing or partial erasure of the printed material on the document. With single sided documents, this does not present a problem as the separator can be designed so that the retard mechanism acts upon the underside of the document. However, with documents printed on both sides, there is no way to avoid the problem. Additionally, the reliable operation of friction retard feeders is highly dependent on the relative frictional properties of the paper being handled. This cannot be controlled in a document feeder.
These problems are aggravated when an attempt is made to feed sheets from the bottom of the stack. However, in may instances it is desirable to provide a bottom feeder to allow restacking of sheets while the feeder is operating or to replenish the sheet supply without shutting off the feeder.
With bottom sheet feeders, since the stack height is variable, the normal force on the bottom sheet, pressing the stack against the bottom sheet and pressing the bottom sheet against the stack tray is variable. To overcome or reduce these forces, air floatation of the stack by providing a perforated tray with positive pressure air supplied thereto or by providing riffle jets at the edges of the stack to inject air between the sheets near the bottom of the stack has been found effective.
It is the object of this invention to provide an improved bottom vacuum feeder.